In recent years, electronic equipment such as an AV device, a personal computer, and a portable communication device is rapidly made portable and cordless, and a hermetically sealed battery which has high energy density and a superior load characteristic is demanded as a driving power source of the electronic equipment and other motive devices. In particular, a lithium battery comes under the spotlight because of such many features that its energy density and voltage is high and shelf life is long.
For example, in order to form a cylindrical lithium battery, an electrode plate group is formed by winding a positive electrode plate and a negative electrode plate in a spiral shape with disposing a separator between them and the electrode plate group is contained in a cylindrical battery case with a bottom. After injecting a predetermined amount of electrolyte into the battery case, a ring-shaped groove-forming processing is carried out on an outside periphery in the vicinity of an opening of the battery case. Then, a sealing plate is inserted and disposed into the opening of the battery case through a gasket, and the rim of the opening of the battery case is crimped inside in a state where the sealing plate is mounted on a ring-shaped support section which is formed in the shape of a protrusion inside the battery case by a groove portion. A positive lead which is pulled out of an upper portion of the electrode plate group is welded to the sealing plate in advance of a sealing process.
There is a proposed method of groove-forming processing on the foregoing battery case in which a core of a top die and a bottom die sandwich and hold the top and bottom of the battery case. While the top and bottom dies rotate the battery case, a protrusion on the outside periphery of a groove-forming roller is pressed against the outside periphery of the battery case to form a groove portion. Also, at this time, pressure is applied to the battery case from above and below in order to restrain reduction in the wall thickness of an upper part of the groove portion (for example, refer to Patent Document 1).
Also, there is another proposed method of groove-forming processing on the battery case in which a bottom die holding the bottom of the battery case moves upward and a core tightly comes into contact with the opening of the battery case to rotate the battery case. In this state, a groove-forming roller is pressed against the outside periphery of the battery case and is pushed into it by a predetermined depth at a constant speed to form a groove portion. Also, at this time, the amount of pushing the bottom die up is adjusted and a wall material is supplied from a side wall of a lower part of the groove portion in order to prevent the end portion of the upper jaw of the groove portion from thinning down (for example, refer to Patent Document 2).
There is further another proposed method of groove-forming processing on the battery case in which the height of a receiving die receiving the bottom of the battery case is varied in accordance with the height of the battery case in order to carry out the groove-forming processing on the various types of battery cases which have the same diameter and different heights (for example, refer to Patent Document 3).
Patent Document 1: Japanese Patent Application Laid-Open No. 9-199092
Patent Document 2: Japanese Patent Application Laid-Open No. 2005-19050
Patent Document 3: Japanese Patent Application Laid-Open No. 2000-21362